To prevent a next paper which is being carried from contacting with a paste application position of a prior paper when piling paper on a stacker, in a paper post-processing device for performing paste-binding as a binding process of a paper bundle.

In the paper post-processing device 1 for carrying printed paper S and guide it to the stacker 17 and folding the bundle of paper by poking a folding knife 18 to a fold position of the bundle of paper piled up on the stacker 17, a slope-like projection part 17a is arranged in the stacker 17 so that a part of paper at an upstream side in a carrying direction from the fold position of the paper S carried to the stacker 17 is projecting to a side of the folding knife 18 from the fold position when applying the paste at the fold position of the paper S.